Isocyanates in the context of the present invention are both conventional isocyanates, which bear NCO groups at aromatic, aliphatic or cycloaliphatic hydrocarbons, and also prepolymers which contain free NCO groups even after reaction of the conventional isocyanates with polyols.
Polyfunctional isocyanates containing two or more NCO groups in particular are highly viscous products. The high viscosity of these products often gives rise to difficulties in the processing of the isocyanates to polyurethanes because the highly viscous isocyanates are difficult to pump and difficult to mix with other components. Accordingly, solvents are added to the isocyanates to reduce their viscosity. Trimeric isocyanurates which are frequently added in the production of polyurethanes are also highly viscous products to which solvents are added to reduce viscosity.
Hitherto, the solvents used have mostly been organic solvents of the halogenated hydrocarbon type, such as methylene chloride, 1,2-dichloropropane; aromatic hydrocarbons, such as toluene; ethers, such as petroleum ether; or even low-viscosity phosphates, such as trioctyl phosphate; trioctyl phosphate also has a plasticizing effect. For ecological and toxicological reasons, however, it is becoming increasingly desirable to replace the unsafe solvents hitherto used by ecologically and toxicologically safer solvents.
It is known from U.S. Pat. No. 2,801,244 that the trifunctional isocyanate trimers of 4-alkyl-m-phenylenediamine diisocyanates can also be dissolved in ethyl acetate. However, ethyl acetate is a highly volatile ester which partly escapes even under the processing conditions.
The problem addressed by the present invention was to provide solvents for isocyanates and isocyanurates which would be toxicologically and ecologically safe and which would be more volatile than ethyl acetate.